Semiconductor device and method for producing a semiconductor device

ABSTRACT

One embodiment describes a method of manufacturing a semiconductor device. Here, impurities are implanted into a semiconductor body via a first side of the semiconductor body. Thereafter, a drift zone layer on the first side of the semiconductor body is formed. The following is an ablation of the semiconductor body from a second side of the semiconductor body and up to pn junction defined by impurities.

RELATED APPLICATIONS

This application claims priority benefit of German Patent Application102011052605.6, which was filed on Aug. 11, 2011. The entire contents ofthe German Patent Application are incorporated herein by reference.

BACKGROUND

The application relates to a semiconductor device and a method forproducing or manufacturing a semiconductor device.

For a variety of applications in which electronic semiconductor devicesand integrated circuits (IC, integrated circuit) are used, it isadvantageous to restrict the total thickness of the semiconductordevices or integrated circuits. For example, low weight and low heightmay be important for smart cards and smart cards applications. Likewise,the electrical properties of, for example vertical power semiconductorcomponents, may be improved by achieving specific settings of thethickness of the semiconductor body.

For this purpose an accurate and reproducible thickness adjustment overthe entire surface of the semiconductor body is desirable in order toavoid yield losses in the manufacture and to ensure reliable electricalproperties of the semiconductor device or the integrated circuit.

SUMMARY

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference number in different instances in thedescription and the figures may indicate similar or identical items.

Embodiments discussed in the following describe a method ofmanufacturing a semiconductor device, which allows reproducible thinningof a semiconductor body of the semiconductor device. Further embodimentsare devoted to such semiconductor devices.

One embodiment relates to a method of manufacturing a semiconductordevice. The method comprises implanting impurities into a semiconductorbody on a first side of the semiconductor body. The method may includeforming a drift zone layer on the first side of the semiconductor bodyand a removal of the semiconductor body from a side opposite the firstsecond side of the semiconductor body up to the pn junction, defined byforeign materials, or a through the pn junction space charge zone or upto the foreign materials dopant concentration.

A semiconductor device according to an embodiment comprises asemiconductor body having a first side and a second side. Thesemiconductor device further comprises a plurality of field stop zones,which are formed within the semiconductor body and down to differentdepths. One or each of a plurality of field stop zones meets a verticaldistance b1 from a maximum of a dopant concentration the respectivefield stop zone at half maximum in the direction of the first side and avertical distance b2 from the maximum of the dopant concentration athalf maximum in the direction of the second side of the relation 0,9<b1/b2<1.1.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference number in different instances in thedescription and the figures may indicate similar or identical items.

FIGS. 1A-1C illustrate schematic cross sectional views of asemiconductor body during a process for manufacturing. A semiconductordevice may be implanted to thereby define a stop of a downstreamstripping process of the semiconductor body.

FIG. 2A-2F illustrate schematic cross sectional views of a semiconductorbody during a process for manufacturing a semiconductor device in whichat least one n-type field stop zone is defined.

FIG. 3 illustrates a cross sectional view of a semiconductor body duringa process for manufacturing a semiconductor device wherein within adrift region of the n-type, a plurality of p-type field stop zones areformed.

FIG. 4 illustrates an alternative embodiment of the schematic crosssection view illustrated in FIG. 2D.

FIG. 5 illustrates an alternative embodiment of the schematic crosssection views illustrated in FIG. 2D and FIG. 4.

DETAILED DESCRIPTION

Exemplary embodiments are described in greater detail with reference tothe figures. The invention is not limited to the specifically describedembodiments but can be suitably modified and altered. Individualfeatures and feature combinations of one embodiment can be customizedwith features and feature combinations of other one or more embodiments,unless this is expressly excluded.

Before the following embodiments with reference to the figures areexplained in detail, it should be noted that matching elements areprovided in the figures with matching or similar reference numerals. Insome cases, the description of such matching or similar referencenumerals will not repeated. In addition, the figures are not necessarilyshown to scale, since their focus is on the illustration and explanationof basic principles.

In the following, a pn junction is defined as a place in a semiconductorbody on which an n-type dopant concentration under p-type a dopantconcentration falls or a p-type dopant concentration under a n-typedopant concentration falls or a combination of p and n dopants.

FIGS. 1A to 1C are schematic cross-sectional views of a semiconductorbody 100 during different process stages of manufacturing asemiconductor device according to an embodiment.

In the schematic cross-sectional view of FIG. 1A, a semiconductor body100 is shown having a first side 101 and a second side 102, wherein theperpendicular direction to the first side 101 and second side 102 isreferred to as the y-direction and the parallel direction of the firstside 101 and the second side 102 is referred to as the x-direction. Thesemiconductor body 100 typically comprises a semiconductor wafer, aso-called “wafer”. The semiconductor wafer can for example be free ofdeposited semiconductor layers or have one or a plurality of layers onthe first side 101 and/or the second side 102. According to oneembodiment, the semiconductor body 100 includes a p-doped semiconductorsubstrate of silicon, i.e. a Si wafer, e.g. with a diameter of 8 inches(200 mm), 12 inches (300 mm) or 18 inches (450 mm).

Foreign materials or impurities 105 are implanted near a surface on thefirst side 101 into the semiconductor body 100. Such foreign materialsmay include, after activation of an n-type and/or p-type doping insilicon, for example, one or a combination of materials including,phosphorus, arsenic, antimony, selenium and sulfur.

As illustrated in FIG. 1B, a drift zone layer 110 may be formed over oron the first side 101 of the semiconductor body 100. The drift zonelayer 110 may for example be epitaxially grown over the first side 101of the semiconductor body 100. A thickness and a dopant concentration inthe drift region layer 110 may be determined based on electricalrequirements of the manufactured semiconductor device, for example basedon a voltage class or on-resistance.

The formation of the drift region layer 110 on the semiconductor body100 including the impurities 105 may occur before formation of one ormore other layers over or in the semiconductor body.

Optionally, a preformed semiconductor layer or one or more layers of thesemiconductor layer stack may be implanted with impurities. Thus, aplurality of field stop zones may be incorporated in a completedsemiconductor component, such as an insulated gate bipolar transistor(IGBT), a diode or a field effect transistor (FET, Field EffectTransistor) or a metal-oxide semiconductor FET (MOSFET,Metal-Oxide-Semiconductor FET), to reduce the electric field and toprevent a “crackdown” of the electric field or the space charge zoneback up to a highly doped region, such as an emitter region. The fieldstop zone or field stop zones of a field stop zone stack may bestructured and formed by a previously implanted field stop zoneimplantation mask, defining impurities on the semiconductor body. Theimplantation mask may, for example, be a photolithographically patternedhard mask or resist mask.

With a lateral structuring of the field stop zone, it is possible todesign a softer shutdown of IGBTs, as a charge carrier discharge can becontrolled by a width and a spacing of the recesses in the field stopzone layer. By way of example, a thickness, in the range between 1micron and 30 microns, or even between 2 microns and 7 microns, of thefield stop zone or a field stop zone in the field stop zone stack may bedefined depending on the choice of the field stop zone impurities and asubsequent use of temperature. Typical implantation energies and dosesof the impurities to the definition of a field stop layer are phosphorus(P) as impurity in the range from 50 keV to 200 keV and 2×10¹¹ cm⁻² to1×10¹³ cm⁻² or 4×10¹¹ cm⁻² to 2×10¹² cm⁻².

The formation of the drift region layer 110 is followed by a processingof the semiconductor body at the first side 101, e.g. at a front side ofthe semiconductor body 100. This further processing provides, forexample, the formation of semiconductor zones within the drift region110. For example, implantation and/or diffusion of impurities into thedrift region layer 110 may provide doped semiconductor regions withinthe drift zone region layer 110, e.g. the formation of an anode of adiode power of body and source of a vertical IGBTs or MOSFETs. Also, theformation of one or more wiring layers with intermediate compounds maybe achieved.

As part of the processing at the first side 101, elements are shown asbeing produced in the simplified schematic cross sectional view of FIG.1B in the form of squares 125 on the first side 101.

As shown in the schematic cross-sectional view of FIG. 1C, a portion ofthe semiconductor body 100 may be removed from the second side 102. Aborder of the ablated area of the semiconductor body 100 isschematically illustrated by a dashed line. A removal direction ismarked with arrows 109. The semiconductor body 100 is preferably removedfrom the second side 102 with an electrochemical etching process,wherein the pn junction and the plane spanned by the pn junction chargespace region is an etch stop for terminating the etching process. Uponreaching this etch stop/stops the etching process terminatesautomatically and is self-aligned in this manner. Thus, a preciseremoval of the semiconductor body 100 from the second side 102 ispossible and thus a precise adjustment of the final thickness of thesemiconductor device may be achieved. This lowers the fluctuations inthe final thickness of the semiconductor device. As an etch stop, forexample, a characteristic change of a current flowing within theelectrochemical etching current is used when reaching the etch stops,i.e. of the pn junction, which is used for terminating the etchingprocess. At the beginning of the removal from the second side 102,mechanical removal methods can also be used.

Electrochemical etching is not required. Rather, etching with a stronglyalkaline medium, such as an aqueous KOH or TMAH solution, may be used.When using boron as the impurity 105 in a weakly p- or n-dopedsemiconductor body 100, a complete impurity implantation may be achievedwith high boron doping (e.g., >10¹⁹ cm⁻³) used as an etch stop.

After the removal of the semiconductor body 100 of the second side 102,up to the impurity 105 defined pn junction or the plane spanned by thepn junction depletion region or up to the impurities 105 defined dopantconcentration, further processing of the body 100 may occur. Forexample, by way of the impurity 105 defined pn junction, thesemiconductor 100 may provide a collector-side emitter of a IGBTs, thecathode-side emitter of a diode or the drain of the MOSFET.

FIGS. 2A to 2F are schematic cross-sectional views of a semiconductorbody during the manufacture of a semiconductor device according toanother embodiment.

The schematic shows a cross-sectional view of a p-type semiconductorsubstrate 200, such as a p-type semiconductor substrate made of Si, withan optional implantation of boron into a surface region on a first side201 of the p-type semiconductor substrate 200.

A schematic profile of implanted boron 215 is shown as a depth accordingto the illustrated y axis and amplitude is shown by the x axis.

As shown in the schematic cross-sectional view of the semiconductorsubstrate 200 in FIG. 2B, a semiconductor layer 220 is formed on thefirst side 201 of the semiconductor substrate 200, e.g. by epitaxialgrowth of the semiconductor layer 220 as a Si layer on a p-type siliconsubstrate. Then, n-type impurities, for example a material or a materialcombination of phosphorus, arsenic, antimony, selenium and sulfur, witha base material made e.g. Silicon, may be implanted on the first side201 into the first semiconductor layer 220 (see, schematicallyillustrated profile 216). The semiconductor layer 220, for example, mayhave a thickness of 1 micron to 10 microns or even from 2 microns to 7microns. Depending on the temperature budget during formation of thesemiconductor layer 220, an annealing process may be provided to providea broadening of the optional boron implantation profile. This is shownin FIG. 2B schematically by a lower relative to peak impurityimplantation of boron and by a comparatively large width of theimplantation profile shown schematically by reference numeral 215.

The semiconductor layer 220 may be patterned, by photolithography forexample, before or after implantation of the n-type impurities into thesemiconductor layer 220.

As shown in the schematic cross-sectional view of FIG. 2C, which will beoptional to the structured first semiconductor layer 220, a secondsemiconductor layer 222 may be formed by epitaxial growth. The second n⁻type semiconductor layer 222 provides a drift zone layer of thesemiconductor device to be formed. A dopant concentration and athickness of the second semiconductor layer 222 is a function of therequirements for the manufactured semiconductor device, such as thenecessary dielectric strength.

As illustrated in the cross-sectional view of FIG. 2D, the formation ofthe drift zone layer constituting the second semiconductor layer 222 maybe on the first side 201, e.g. a front side. Impurities may beintroduced into the semiconductor body, e.g. by implantation and/ordiffusion, which are defined or buried in the layer 201 and the firstsemiconductor zones ranging from n-type and/or p-type. Depending on thenature of the manufactured semiconductor device, for example a diode,field effect transistor, and bipolar transistor, these furthersemiconductor zones may be associated with source, body, and/or anodeemitters. A wiring portion may also be applied to the first side 201,e.g. by forming one or more conductive layers, such as metallization,which is structured as a wiring pattern, e.g. as a line track pattern,and between which there may be intermediate dielectric layers. Aconductive connection between conductors at different levels can begenerated, for example, through contact openings in the interlayerdielectric layers.

As part of the processing at the first side 201, elements may beproduced and are shown in the form of squares 225 over the first side201.

As shown in FIG. 2E, a thinning of the semiconductor substrate 200 maybe performed from the second side 202. The removal of the semiconductorbody 200 may be achieved using an electrochemical process, including then-doped profile 216 and the p-doped profile 215 defined pn junction (seeFIG. 2D) or its space charge zone. The removal of the semiconductor body200 may also take place in an alkaline etching and terminate at thepreviously introduced boron-doped layer. Thus, a precise removal of thesemiconductor body 100 of the second side 202 may be achieved, whereby alowering of the fluctuations in the final thickness of the semiconductordevice is achieved.

As shown in FIG. 2F, processing may be performed to the second side 202.In one example, a produced highly doped layer is produced in a region229 by implantation of corresponding impurities from the second side202. Such a layer may include, for example, a cathode of a diodeemitter, a highly doped drain region of a FET or a collector sideemitter of an IGBT. Similarly, a training connection or a contact layersuch as a metal layer may be provided on the second side 202. If thep-doped layer region 215 serves as an etch stop, this doping layerregion can also be seen as p-doped emitters.

Alternatively to the FIG. 2C embodiment having a first semiconductorlayer 220 and a drift zone layer constituting the second semiconductorlayer 222, an embodiment, as shown in FIG. 3 shows a schematiccross-sectional view, may include a layer stack having first to fourthfield stop zones 220 a, 220 b, 220 c, 220 d formed, for example, beforethe drift region layer 222 is formed. In the illustrated example, thelowest field stop zones 220 a, 220 b may be differently structured. Ofcourse, these layers can be formed unstructured. By structuring thefield stop zone layers 220 a, 220 b, for example, a softer switching offof IGBTs may be achieved, in particular by controlling the chargecarrier discharge means provided by the width and spacing of therecesses in one or more of the field stop layers. The field stop zones220 a, 220 b, 220 c, 220 d can, for example, be produced in successivelygrown semiconductor layers 235 a, 235 b, 235 c, 235 d by masked orunmasked implantation of impurities, the respective implantation isperformed for example by deposition of each individual layer. Accordingto one embodiment a width d1, d2, d3, d4 and a dopant concentration 216a, 216 b, 216 c, 216 d of the first through fourth field stop zones 220a, 220 b, 220 c, 220 d varies based on a distance from the substrate200. This relationship is captured by d4<d3<d2<d1. Likewise, anamplitude N1, N2, N3, N4 of the dopant concentration in the first tofirst to fourth field stop zones 220 a, 220 b, 220 c, 220 d varies basedon a distance from the semiconductor substrate 200. This relationship isrecognized by N4<N3<N2<N1. The four field stop zones, 220 a, 220 b, 220c, 220 d may formed for example by matching dose. In such a case, therelationship d4<d3<d2<d1 may be around one in a particular example.According to another embodiment, a width d1, d2, d3, d4 of the dopantconcentration 216 a, 216 b, 216 c, 216 d of the first through fourthfield stop zones 220 a, 220 b, 220 c, 220 d are of increasing depth,i.e. with increasing distance from the semiconductor substrate 200. Thiscase arises for example when a temperature budget for generating thefield stop zone is negligibly small compared to the formation of thefield stop zones.

The dopant profiles, for example, have different profiles produced byproton irradiation of an approximately Gaussian distribution. For eachof the plurality of field stop zones, the relationship: 0.9<b1/b2<1.1 or0.95<b1/b2<1.05 may be true. In FIG. 3 an example four field stop zones220 a, 220 b, 220 c, 220 d are shown. Off course, the number of fieldstop zones is chosen by way of example only. Other numbers of field stopzones may be used as well (e.g., 1, 2, 3, 5, 6 and 7).

As an alternative to the embodiment shown in FIG. 2D can, as shown inFIG. 4 and in addition to that the shown in FIG. 2A that includesimplantation of boron into the semiconductor substrate 200 (seeassociated profile 217 in FIG. 4), a further implantation of n-typeimpurities be carried out, were the n-type impurities are preferablyimplanted deeper into the semiconductor substrate 200 as the impurityboron (see associated profile 217 in FIG. 4). Such an additionalimplantation may be useful, for example, in the preparation of an IGBT.The removal of the substrate 200, in one example electrochemically, to apn junction 230 that is formed by n-type impurities in the formed n-typesemiconductor region 233 and the p-type semiconductor substrate 200.Subsequently, the implanted, by way of n-type impurities, and formedn-type semiconductor region 233, may be removed by alkaline etching, tothe boron produced p+-type semiconductor layer 234. This p+-typesemiconductor layer 234 serves as a collector side emitter of the IGBTand is generated approximately, a described in relation to FIG. 2A, bysuitable choice of implantation dose and energy.

As shown in FIG. 5, as an alternative embodiment, an n+-typesemiconductor layer 237 in the semiconductor substrate 200 may be usedbelow the semiconductor layer 220, e.g. under the implantation processshown in FIG. 2A, in which case boron as an n-type impurity isimplanted.

Removal of the semiconductor substrate 200 may be achieved using anelectrochemical process and ends at the pn junction 230′. The remainingn+-type semiconductor layer 237 may serve as a cathode emitter of adiode or as a drain of a FET. Thus, a precise removal of thesemiconductor substrate 200 is possible and thus a precise adjustment ofthe final thickness of the semiconductor device, whereby a lowering ofthe fluctuations in the final thickness of the semiconductor device maybe achieved.

For the purposes of this disclosure and the claims that follow, theterms “coupled” and “connected” have been used to describe how variouselements interface. Such described interfacing of various elements maybe either direct or indirect. Although the subject matter has beendescribed in language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features or acts described. Rather, the specific features andacts are disclosed as preferred forms of implementing the claims. Thespecific features and acts described in this disclosure and variationsof these specific features and acts may be implemented separately or maybe combined.

The invention claimed is:
 1. A method of manufacturing a semiconductordevice, comprising: implanting impurities in a semiconductor body via afirst side of the semiconductor body; forming a drift zone layer on thefirst side of the semiconductor body; and removing at least a portion ofthe semiconductor body from a second side of the semiconductor bodybeing opposite of the first side, the removing of the semiconductor bodyterminating at least at a pn junction defined by the implantedimpurities, wherein prior to implanting the impurities, forming asemiconductor layer on the first side of the semiconductor body; andimplanting impurities in the semiconductor layer.
 2. The method of claim1, further comprising performing a plurality of impurity implanting actsthereby forming a layer stack have a plurality of layers with implantedimpurities.
 3. The method of claim 2, wherein an implantation dose ofimpurities for a first layer of the plurality of layers is greater thanan implantation dose of impurities for a second layer of the pluralityof layers.
 4. The method of claim 2, wherein a width of an implantationprofile of impurities in the plurality of layers of the layer stackdecreases with increasing distance of a respective layer to the secondside of the semiconductor body.
 5. The method according to claim 2,wherein the impurities introduced into the semiconductor layer or in atleast a semiconductor layer of the layer stack are introduced via animplant mask.
 6. The method according to claim 1, wherein thesemiconductor layer or the semiconductor layers of the layer stack eachhave a thickness in the range between 1 micron and 10 microns.
 7. Themethod according claim 1, wherein a semiconductor substrate of thesemiconductor body as a p-doped silicon substrate.
 8. The method ofclaim 7, wherein prior to implanting the impurities into thesemiconductor body, boron is implanted into the semiconductor body viathe first side, whereby the boron is first implanted into thesemiconductor body followed by performing the act of implanting theimpurities into the semiconductor body.
 9. The method according claim 1,wherein after the removal of at least a portion the semiconductor body,further comprising implanting further impurities into the semiconductorbody.
 10. The method according to claim 1, wherein after the removal ofat least a portion of the semiconductor body, defusing furtherimpurities into the semiconductor body.
 11. The method according toclaim 1, wherein the impurities are from one or more of the materialsphosphorus, arsenic, antimony, selenium, sulfur.
 12. The method of claim1, wherein after the removal of at least a portion of the semiconductorbody no further implantation of impurities into the semiconductor bodyis performed.
 13. The method of claim 12, wherein the semiconductordevice is formed as insulated gate bipolar transistor and implanting theimpurities into the semiconductor body of silicon is carried out withboron as an impurity.
 14. The method of claim 13, wherein the boron isimplanted prior to depositing a first semiconductor layer on asemiconductor substrate of the semiconductor body of.
 15. The method ofclaim 13, wherein after the deposition of a first semiconductor layer ona semiconductor substrate of the semiconductor body the boron isimplanted into the first semiconductor layer over the first side. 16.The method according to claim 13, further comprising implanting ann-type impurity into the semiconductor body via the first side and, animplantation depth of the n-type impurity to the first side is greaterthan an implantation depth of boron.
 17. The method according to claim1, wherein the semiconductor device is formed as a diode ormetal-oxide-semiconductor field effect transistor and implanting theimpurities into the semiconductor body of silicon includes implanting ann-type impurity material.
 18. The method according to claim 1, whereinafter the implantation of impurities into the semiconductor body andprior to forming the drift zone layer, a surface region on the firstside is melted for limited duration and recrystallized.
 19. Asemiconductor device comprising: a semiconductor body having a firstside and a second side; one or a plurality of field stop zones areformed within the semiconductor body, the one or each of the pluralityof field stop zones having a vertical distance b1 from a maximum of adopant concentration to a half maximum of the one or each of theplurality of field stop zones in the direction of the first side and avertical distance b2 from the maximum of the dopant concentration to thehalf maximum in the direction of the second side of the semiconductorbody, wherein 0.9<b1/b2<1.1.
 20. The semiconductor device according toclaim 19, wherein the one or at least one of said plurality of fieldstop zones is in a plane parallel to the first and second sides.
 21. Thesemiconductor device according to claim 19, wherein a width of thedopant concentration in the depth direction in the plurality of fieldstop zones is in the range 1 microns to 30 microns.
 22. Thesemiconductor device according to claim 19, wherein the semiconductordevice is an IGBT, a MOSFET or a diode.
 23. The semiconductor deviceaccording to claim 19, wherein the dopant concentration of adjacentfield stop zones of the plurality of field stop zones overlap.